Usually small bouncy castles have 2 pipes, so do we need to connect 2 air blowers? No, small bouncy castle usually only need to be connected with one tube, another tube is used to help deflate and must not connect to the second fan.
Larger inflatables may require a second blower and an extra circuit to keep them inflated. Blowers between 1HP and 2HP are often used to keep bouncy castles inflated. Larger inflatables even require multiple blowers or larger blowers to push the required amount of air. Large commercial inflatable water slides and inflatable obstacle courses often use 1.5 HP to 2 HP blowers.
So, what size blower do you need for your inflatables?
It is usually assessed in terms of the amount of air the blower blows per minute. Each unit of CFM is equivalent to blowing 1 cubic foot of air from the blower in one minute. The higher the number, the faster your bounce house will inflate and the firmer it will be during use. There are no hard and fast rules on what size blower you need to use. In general, the bigger the bouncy castle, the higher the CFM you need (and possibly more horsepower).
Another simple way is to check the weight of the inflatable. Usually, the heavier weight, the more horsepower and number of blowers are required.